EFFECTS OF FEEDING FODDER BEET AND CONCENTRATES WITH DIFFERENT PROTEIN CONTENTS ON DAIRY-COWS OFFERED SILAGE AD-LIBITUM

In two changeover design experiments, fifteen early- and sixteen late-lactation cows were used to investigate the effects of offering food beet with ad libitum grass silage and concentrates with different CP content on milk yield and quality. In Experiment 1 (early lactation) cows were offered no fodder beet (0) or 4 kg DM d-1 (4) in conjunction with one of three concentrates containing 159, 191 or 244 g CP kg-1 DM (L,M,H,). Treatments were therefore IL/0, IL/4, IM/0, IM/4, IH/0 and IH/4. In Experiment 2 (late lactation) cows were offered the same level of fodder beet in conjunction with two concentrates containing 129 and 229 (L,H) g CP kg-1 DM. Treatments were therefore 2L/0, 2L/4, 2H/0 and 2H/4. In both experiments feeding fodder beet reduced silage DM intakes (P<0.001) and increased total DM intake (P<0.05 to P<0.001). The substitution rate (r) ranged from 0.46 to 0.59 kg of silage DM (kg-1 fodder beet DM). In Experiment 1, fodder beet tended to increase milk yield, composition and yield of constituents, but the effect was statistically significant for milk protein content only (P<0.01). In Experiment 2, milk yields for 2L/0, 2L/4, 2H/0 and 2H/4 were 11.3, 12.1, 11.7 and 12.5 kg d-1 respectively (s.e.d. 0.43, non-significant), fat contents were 44.4, 47.3, 44-3 and 46.8 g fat kg-1 respectively (s.e.d. 0.73, P<0.001), protein contents were 34.3, 35.6, 35.3 and 36.2 g protein kg-1 respectively (s.e.d. 0.28, P<0.001), fat yields were 494, 574, 512 and 579 g fat d-1 respectively (s.e.d. 20, P<0.001) and protein yields were 385, 426, 407 and 442 g protein d-1 (s.e.d. 13, P<0.01) respectively. Increasing CP in the concentrate significantly increased milk yield in Experiment 1 (23-9, 22-5, 23.5, 23.8, 26.2, 26.5 kg d-1 for 1 L/0, 1 L/4, 1 M/0, IM/4, IH/0 and IH/4 respectively, P<0.05). Higher CP in concentrate also resulted in significantly increased milk protein yield in early-lactation (P<0.001) and milk protein content in late-lactation (P<0.01) cows. There was a significant interaction between fodder beet and concentrate CP content for milk protein yield (P<0.001) in Experiment 1.